The best thing to do would be to get it annoed, which is a paint process that you would get someone to do.
You could spray paint it if you want to go the cheap route, but your gonna find out you get what you pay for.

Anno is the way but it you really want to paint it and take your time with it you do this.
Strip off all current paint/anno/powdercoat
Spray with primer maybe two coats total
sand down primer to a smooth even surface
spray base coat of what ever color you want
****Keep in mind the base will affect the end product....Dark base= Bold End color.......Light Base= Pastel color*****
Place painted surface next to a heat source for 1 hr.
Spray with 2nd coat of base
place next to heat source for 1 hr
Spray either a new color or same color
****if using same color this is the last coat*****
Place next to heat source
****If multiple colors repeat as needed****